Biosurfactants are of great interest due to the demand for natural products with low toxicity. Strain AL 1.1, isolated on Deception Island (Antarctica) and identified as Bacillus licheniformis, produce lipopeptide when grow under a variety of carbohydrates. The lipopeptide was characterised as lichenysin (LchAL1.1). The LchAL1.1 reduced surface tension to 30 mN/m and had a critical micelle concentration of 15 mg/L. This highly effective and efficient characterized the product as a powerful surfactant. Besides, the formation of liquid crystalline by LchAL1.1 in form of Maltese crosses was revealed. This suggested important properties to self-aggregate and opens an important field in the compounds encapsulation.
Nevertheless, their production is not competitive when cost is a limiting factor. For this reason, an economical medium, containing molasses, was optimized to enhance lichenysin production by response surface methodology (RSM). A production of 3.2 g l-1 of lichenysin was achieved with an optimum medium containing 107.82 g l-1 of molasses, 6.47 g l-1 of NaNO3 and 9.7 g l-1 of K2HPO4/KH2PO4, in which, molasses and phosphate salts had a significant effect on biosurfactant production. This medium resulted in a fifteen times increase in production compared with the non-optimized medium.
The LchAL1.1 showed a weak antimicrobial activity, however, it had notable anti-adhesion activity, and was able to prevent and eliminate the biofilm formation by pathogenic strains associated with foodborne illness. Lychenysin was effectively applied in a surface pre-treatment to avoid microbial biofilm. It was also very efficient in removing biofilms in surface post-treatment. In addition, the molecular mechanism underlying permeabilization of model and biological membranes by the lipopeptide lichenysin was evaluated. The LchAL1.1 caused hemolysis of human erythrocytes, which varied with LchAL1.1 concentration in a sigmoidal manner. The LchAL1.1-induced K+ release from red blood cells preceded the leakage of hemoglobin, and in addition, hemolysis could be impeded by the presence of compounds in the external medium having a size larger than PEG 4000, indicating a colloid-osmotic mechanism for hemolysis. Lichenysin also caused permeabilization of model phospholipid membranes, as monitored by the release of carboxyfluorescein, from large unilamellar vesicles (LUV). Lipid membrane composition plays a role in the target membrane selectivity of lichenysin. The experimental results support a pore-type behaviour that can be explained by the formation of enhanced permeability domains in the erythrocyte membrane, as observed in model membranes. Furthermore, the LchAL1.1 induced apoptosis in non-differentiated intestinal Caco-2 cells (96.5%). The action can be due to the micelles interaction with lipid bilayer, because the effect occurred to LchAL1.1 concentration above critical micelle concentration (50-100 µg ml-1).
Finally, the interaction between lichenysin, arginine (C3(LA)2) and lysine (C6(LL)2) surfactants was evaluated. Thus, when the LchAL1.1 act as co-surfactant improved the antimicrobial activity of arginine (C3(LA)2) surfactant, showing a synergistic effect, mainly in front to Gram negatives bacteria.